Custom Classes : general questions

Hello,

I'm quite a newbie on CI4 and I've got general questions.

Few years ago, I've created a php class that helps me to create a small CMS and build my contents. It creates for me the html form to manipulate my tables easily (add and remove tables, add and remove lines, add fields, resort, hide elements)... a bit like phpmyadmin but much simpler, specific to my app (I can chose how I want to edit my tables), and visually more ergonomic. Actually my class did the model-view-controller for me.

Now I want to go on with CodeIgniter and adapt my php class on CI4 to get a better "structure". 

1 - What do you think about creating a class that I can use in many Models, Views and Controllers ? 
2 - Where should I put this class "for a good practice" and call it if I would like to use it with several controllers, models and views ? 
3 - And last question : Does something already exists like that ? ... A plugin in CodeIgniter4 for adding quickly content in databases ?

Thank you a lot for your help !